Principles of Dietetics: Nutrient Science and Reference Standards
Core science to own
Dietetics questions reward precise definitions. Know the energy yields (carbohydrate 4, protein 4, fat 9, alcohol 7 kcal/g), the digestion and absorption map (little carbohydrate digestion in the stomach; fat emulsified by bile in the duodenum; most absorption in the jejunum; vitamin B12 bound to intrinsic factor and bile salts reclaimed in the terminal ileum; water and electrolytes in the colon), and protein quality concepts (limiting amino acid, complementary proteins, PDCAAS, DIAAS).
Standards and reference values
Separate the DRI family: EAR is the median requirement, used for population prevalence estimates; RDA is EAR plus 2 SD and covers 97–98% of healthy people; AI is used when data are too thin to set an EAR; UL is the highest intake unlikely to cause harm, not a toxicity threshold; AMDR and EER round out the set. Expect AMDR percentages: carbohydrate 45–65%, fat 20–35%, protein 10–35% of energy.
Traps
Swapping EAR and RDA when a question asks about an individual's requirement versus a recommendation. Treating the UL as a target. Assuming every water-soluble vitamin is un stored (B12 is stored in the liver). Blurring mineral interactions - calcium and phosphorus, iron–zinc–copper competition, phytates and oxalates limiting mineral absorption. Ignoring bioavailability when comparing heme with non-heme iron, or natural folate with synthetic folic acid.
Worked example
A 2,000 kcal diet with 60% of energy from carbohydrate: 2,000 × 0.60 = 1,200 kcal, divided by 4 kcal/g = 300 g carbohydrate. At 15% protein: 300 kcal ÷ 4 = 75 g. Always convert percentages to grams before comparing against gram-based goals.